Assessment of Changes in Udder Half Defects over Time in Non-Dairy Ewes.

A total of 1039 non-dairy breed (Romney) ewes were enrolled in two studies to assess the changes in udder half defect status (hard, lump, or normal) over time and to predict the risk of future udder half defect occurrence. In the first study (study A), udder halves of 991 ewes were assessed utilizing a standardized udder palpation method and scored four times a year, for two successive years (pre-mating, pre-lambing, docking, and weaning). The second study (study B) assessed the udder halves at pre-mating, and at six weekly intervals in the first six weeks of lactation in 46 ewes that had defective and normal udder halves. Udder half defect change over time was visualized via lasagna plots, and multinomial logistic regression was used to predict the risk or probability of udder half defect occurrence. In the first study, the highest occurrence of udder halves categorised as hard was observed at either pre-mating or docking. Udder halves categorised as lump had their highest occurrence at either docking or weaning. Udder halves detected with a defect (hard or lump) at pre-mating were more likely (RRR: 6.8 to 1444) to be defective (hard or lump) at future examinations (pre-lambing, docking, or weaning) within the same year or pre-mating the following year, compared to udder halves categorised as normal. In the second study, the change of udder half defect type over the first six weeks of lactation was variable. However, it was observed that the udder half defects, particularly udder halves categorised as hard, decreased during lactation. Failure to express milk in udder halves in early lactation was associated with a higher occurrence and persistency of udder half defects. In conclusion, the occurrence of diffuse hardness or lumps in an udder half changed over time, and the risk of future occurrence of a defect was higher in udder halves previously categorised as either hard or lump. Hence, it is recommended that farmers identify and cull ewes with udder halves categorised as hard and lump.

Factors Associated with Mortality of Lambs Born to Ewe Hoggets.

The reproductive performance of ewe hoggets is poorer than that of mature-age ewes due to production of fewer lambs with poorer survival. Scant data are available on the risk factors for, and causes of, the mortality for lambs born to ewe hoggets, the impact of ewe deaths on lamb loss, and the causes of death for lambs born to ewe hoggets vs. mature-age ewes lambing in the same circumstances. In this study, 297 lambs born to 1142 ewe hoggets were necropsied along with 273 lambs born to 1050 mature-age ewes. Low lamb birthweight, multiple litter size, and increasing ewe hogget average daily gain from breeding to late pregnancy were risk factors for lamb mortality. The most common cause of mortality for lambs born to ewe hoggets was stillbirth and the risk factors for stillbirth were similar to those for lamb mortality generally. Approximately 11% of ewe hoggets' lamb deaths were due to the death of the dam. Causes of mortality differed between lambs born to ewe hoggets vs. those born to mature-age ewes. Management practices to increase ewe hogget lambs' birthweights (particularly those from multiple litters) and supervision of ewe hoggets at lambing time are recommended.

Effect of Palpable Udder Defects on Milk Yield, Somatic Cell Count, and Milk Composition in Non-Dairy Ewes.

In non-dairy ewes, udder defects hinder the survival and weight gain of their pre-weaned lambs. The objectives of this study were to determine the effects of palpable udder defects on milk yield, somatic cell count (SCC), and milk composition in non-dairy Romney ewes. Ewes with a history of udder defects or normal udders were selected for the study. Of a total of 48 ewes that lambed, 30 ewes reared at least one lamb, and were milked six times, once weekly, for the first six weeks of lactation. Udder halves were palpated and scored at each milking event. Multivariate linear mixed models examined the impacts of udder defects on udder-half and whole-udder milk yield, SCC, and milk composition (fat, protein, lactose, total solids, and solids non-fat (SNF)). Across the six examinations, 24.7% of the total 352 udder-half examinations were observed to be defective. Udder halves that were defective at least once produced on average 57.9% less (p < 0.05) milk than normal udder halves, while normal udder halves with a contralateral defective half yielded 33.5% more (p < 0.05) milk than normal udder halves. Successive occurrence of both hard and lump udder defect categories in an udder-half, udder defect detection early in lactation, and a high frequency of udder defect detection were all associated with udder-half milk yield loss (p < 0.05). At the whole-udder level, no differences in milk yield (p > 0.05) were observed between those with one udder-half defective and both normal udder-halves. However, udders in which one udder half was categorised as hard but progressed to lump and remained as lump until 42 days of lactation produced less (p < 0.05) milk compared with normal udders. With the exception of SNF, there were no significant associations (p > 0.05) between milk composition parameters and udder defect. Overall, these findings emphasise the importance of udder health in non-dairy ewes and the potential effect of udder defects on their lambs.

Ewe Wastage in New Zealand Commercial Flocks: Extent, Timing, Association with Hogget Reproductive Outcomes and BCS.

Ewe wastage is the combination of on-farm mortality and premature culling. Internationally, there is limited research on actual wastage incidence and causes in commercial sheep flocks. To the authors' knowledge, this is the first study that reports both lifetime wastage and detailed annual wastage in a sample of commercial New Zealand flocks. This study utilized data collected from 13,142 ewes from four cohorts on three commercial New Zealand farms (Farm A 2010-born, Farm A 2011-born, Farm B, Farm C), during the period 2011-2017, as they aged from replacement hoggets to 6-year-old ewes (Farm A and Farm B) or 3-year-old ewes (Farm C). Data collection visits occurred at three or four key management times each year, namely pre-mating, pregnancy diagnosis, pre-lambing and weaning. At each visit, body condition score (BCS) was assessed and any ewes that were culled or had died on farm were recorded. As this was a lifetime study, each ewe was assigned an outcome and corresponding 'exit age'. By the end of the study, all ewes that had exited their respective flocks, were classified as either prematurely culled, or dead/missing, or if still in the flock, as censored, and either the exact date or interval in which they exited the flock was recorded. Semi-parametric competing risk (premature culling vs. dead/missing), interval-censored survival models were developed to: 1. describe the association between hogget reproductive outcomes and risk of subsequent wastage, and 2. assess pre-mating BCS as a predictor of wastage in that production year. Of the 13,142 enrolled ewes, 50.4% exited their respective flocks due to premature culling and 40.0% due to on-farm dead/missing, giving a total of 90.4% that exited due to wastage. Annual mortality incidence ranged from 3.5 to 40.2%. As a hogget, wastage incidence ranged from 7.6 to 45.4%. Pregnancy or rearing a lamb as a hogget did not increase risk of subsequent wastage. In all years, pre-mating BCS was a predictor of ewe wastage, with odds of wastage lower with increasing BCS. Therefore, farmers should focus on improving pre-mating BCS to 3.5/5.0 by assessing ewe BCS at weaning, allowing poorer-BCS ewes to be managed to gain BCS before re-breeding.

Effects of natural infection by L. borgpetersenii serovar Hardjo type Hardjo-bovis and L. interrogans serovar Pomona, and leptospiral vaccination, on sheep growth.

In New Zealand, up to 97% of NZ sheep flocks are seropositive to Leptospira borgpetersenii serovar Hardjo and/or Leptospira interrogans Pomona, yet vaccination is rare. This study evaluated the impact of exposure to these serovars and of vaccination on sheep growth. One third of 2260 ewe lambs on eight farms were randomly selected and vaccinated with a primary and booster bivalent Hardjo and Pomona vaccine starting at one month of age on seven farms and at around five months of age on one farm. Repeated blood samples were taken over one (n = 6 farms, bred as ewe lambs at 7-8 months of age) or two (n = 2 farms, bred as rising 2-year-old ewes) years and tested by microscopic agglutination test to assess exposure to Hardjo and Pomona. Individual weights were recorded at the same time and modelled using a multilevel linear model accounting for within-farm clustering and repeated measures. Predicted average weights were computed and compared based on the vaccination status and within the control group based on exposure status (positive for Hardjo only, Pomona only, Hardjo and Pomona and negative) for each combination of farm and weighing episode. Statistical significance of the comparison was evaluated after adjustment for multiple comparisons. There was no difference in average weight between vaccinated and control sheep before or after vaccination in any of the flocks. The comparison between sheep seropositive for either or both serovars and seronegative sheep was inconclusive, with variations of direction and magnitude of the difference between farms and weighing episodes. In the absence of an overall growth response to vaccination, widespread adoption of vaccination would unlikely yield an economic response at the industry level. However, the inconsistency observed when comparing animals based on their exposure status suggests that the actual effect of leptospirosis on growth is difficult to predict. A study of the effect on sheep reproduction is needed to fully assess the effect of vaccination on sheep production.

Effects of natural infection by L. borgpetersenii serovar Hardjo type Hardjo-bovis, L. interrogans serovar Pomona and leptospiral vaccination on sheep reproduction.

Most New Zealand sheep flocks are seropositive to Leptospira serovars Hardjo and/or Pomona, yet vaccination is rare. This study evaluated the impact of exposure to these serovars and of vaccination, on primiparous one- (P1) and two-year-old (P2) sheep reproduction outcomes. The study was designed as a split-flock vaccination trial, with a third of the animals vaccinated starting at one month of age. Reproduction outcomes were the proportion of bred P1 (7 months old) and as P2 (19 months old) scanned pregnant, the proportion of pregnant ewes rearing a lamb to tail docking and the proportion of docked lambs that were weaned. Odds ratios and their 95% confidence intervals were calculated to compare reproductive performance between vaccinated and control sheep, and within the control group, between seropositive and seronegative sheep. Odds ratios (OR) were also calculated to assess the relationship between vaccination and loss to follow-up. There was no difference in pregnancy and docking rates between vaccinated and control sheep, or between seropositive and seronegative sheep. P1 with a Hardjo titre ≥1536 were significantly less likely (OR = 0.41, 95%CI = 0.19-0.93) to keep a lamb between docking and weaning than P1 with both Hardjo and Pomona titres <1536, for an observed difference in weaning rate of up to 22.6% points on one farm. A reduction of weaning rates in 2-tooths seropositive for Pomona alone and both Hardjo and Pomona was observed but this was non-significant, possibly because of a lack of power. No difference in weaning rate was observed between vaccinated and control P1 or P2. On one farm vaccinated P1 were less likely to be lost to follow-up (OR = 0.27, 95% CI 0.08 to 0.95) between breeding and weaning. Comparing reproductive performance of vaccinated and control sheep revealed no significant difference. However, comparing exposed and non-exposed ewes revealed a possible adverse effect of Leptospira on weaning rates. This suggests that a full vaccination program may result in an improvement of reproductive outcomes, possibly by providing herd immunity.

Effectiveness of a commercial leptospiral vaccine on urinary shedding in naturally exposed sheep in New Zealand.

L. borgpetersenii serovar Hardjo and L. interrogans serovar Pomona are endemic in New Zealand sheep. An effective vaccine and vaccination strategy would protect both humans and livestock. Four to 12 lambs were selected from each of eight farms (total=84, vaccinated group), while four to 16 lambs (total=98) served as unvaccinated controls. A commercial Hardjo/Pomona vaccine was given at 1-6 weeks of age, 5-11 weeks later and 33-67 weeks later on seven farms and at 18 weeks of age and 5 weeks later on the eighth farm. Vaccinates and controls were grazed together. Blood was regularly collected from the control group to assess flock exposure. Urine was collected from both groups 26-82 weeks after the second vaccination and tested by quantitative PCR. Seroprevalence in controls at the time of urine sampling ranged from 2.7 to 98.2% for Hardjo and from 0 to 54.1% for Pomona with seroconversion occurring 13 to 67 weeks after the second vaccination in all but one farm where exposure had happened by the time of vaccination. The shedding prevalence adjusted for clustering in farms was 45.1% [95% CI 17.6-72.7] (for an observed number of 50/98) in the control animals and 1.8% [95% CI 0.0-10.1] (for an observed number of 5/84) in the vaccinated animals. The vaccine was 100% effective on five farms where animals were vaccinated before 12 weeks of age and before natural exposure occurred, but the effectiveness was 80% [0-97] on one farm where the lambs were exposed before vaccination and 65% [9-87] to 80% [0-97] on one farm where the animals were fully vaccinated by 24 weeks of age. The overall vaccine effectiveness was 86.3% [63.6-94.8%] despite maternal antibodies in some flocks at first vaccination. Vaccination timing seemed to be crucial in achieving optimum reduction in shedding in urine in vaccinated sheep.

Experimental infection of New Zealand Merino sheep with a suspension of Mycobacterium avium subspecies paratuberculosis (Map) strain Telford: Kinetics of the immune response, histopathology and Map culture.

A long-term study was undertaken to monitor immune responses, faecal cultures and clinical disease in sheep experimentally infected with Mycobacterium avium subspecies paratuberculosis (Map) strain Telford. New Zealand Merino lambs (N=56) were challenged with three oral doses of Map suspension. The lambs were weighed and faecal and blood samples obtained at different time-points. At 63 weeks post-challenge, surviving sheep were euthanised and samples of liver, ileo-caecal valve and mesenteric lymph node were collected for histopathology and Map culture. High IFN-γ and antibody responses were evident as early as 8 weeks post-C1 which persisted until the end of the trial. Approximately 92% of the sheep shed Map in faeces at 36 weeks post-challenge, with the prevalence decreasing to around 40% at the end of the trial. Thirteen sheep progressively lost weight and were euthanised between weeks 32 and 58 post-challenge. Nearly 58% of surviving sheep exhibited histo-pathological lesions in at least one of the three tissues sampled, while 42% showed acid-fast bacilli in at least one tissue. A positive Map culture in at least one tissue was obtained from approximately 85% of sheep. These results indicate that the three doses of Map challenge were highly effective in establishing Johne's disease in NZ Merino lambs.

Control of Brucella ovis infection in sheep.

Approach to control of Brucella ovis would vary in different countries and areas depending on farm and flock characteristics and economic factors. Eradication by a test-and-slaughter approach is the most desirable option in areas where it is logistically and financially feasible. Vaccination is used in areas with a high incidence of infection where eradication would be difficult. Voluntary accreditation programs have been established in some countries and are of particular benefit to pedigree ram breeders.